Hydrothermal growth or "culturing" of quartz has been practiced for many years and has presently been refined to a point where virtually all quartz used for frequency control applications today is cultured quartz. In the commonly practiced commercial process for the hydrothermal growth of quartz, a vertical autoclave holds a supply of quartz nutrient in a bottom portion and is filled to some fraction of its free volume with a solution of sodium hydroxide or sodium carbonate. The upper portion of the autoclave includes a plurality of quartz seed crystals supported by a seed rack. After filling, the autoclave is sealed and then heated to increase the temperature and pressure sufficiently to cause the nutrient to dissolve into solution and thereafter be deposited upon the seed crystals. The autoclave is maintained in this condition for a number of days until crystals of a desired size are grown. A perforated metal disc termed a "baffle" is often within the vessel to separate the dissolving and growth zones and to help in localizing a temperature differential between those two zones.
A discussion of the conventional techniques for cultured quartz growth is contained in R. A. Laudise, "Hydrothermal Growth," in Crystal Growth: An Introduction, P. Hartman, ed., North Holland Pub. Co., 1973, pp. 162-197. Autoclaves used for the commercial production of quartz are made from steel. Such commercial quartz, after being subsequently cut and etched, customarily exhibits on the order of 50-500 etch channels per cm.sup.2. Discussions of etch channel density in quartz may be found in: J. F. Balascio and N. C. Lias, "Standard Characterization Methods for the Determination of the Quality of Hydrothermally Grown Quartz," Proc. 37 th Annual Frequency Control Symposium, 1983, pp. 157-163, and J. F. Balascio and N. C. Lias, "Factors Affecting the Quality and Perfection of Hydrothermally Grown Quartz," Proc. 34th Annual Frequency Control Symposium, 1980, pp. 65-71. Another problem with cultured quartz is that it contains small particulate inclusions. The particles are typically made of sodium iron silicates.
Those concerned with the growth of high perfection quartz for use in precise frequency control and other application have consistently sought to reduce the etch channel and inclusion densities of their product. Various techniques for growing high perfection quartz in limited quantities have been explored and exhibited limited success. A discussion of these techniques is contained in: R. L. Barns, et al., "Dislocation-free and Low-Dislocation Quartz Prepared by Hydrothermal Crystallization," , Journal of Crystal Growth, 43, 1978, pp. 676-686; D. F. Croxall, et al., "Growth and Characterization of High Purity Quartz," Proc. 36th Annual Frequency Control Symposium, 1982, pp. 62-65; A. F. Armington and J. F. Balascio, "The Growth of High Purity, Low Dislocation Quartz," Proc. 38th Annual Frequency Control Symposium, 1984, pp. 3-7. The Barns et al. publication describes the growth of quartz in noble-metal-lined autoclaves. The publication by D. F. Croxall et al. describes crystal growth in an autoclave whose internal surfaces were coated with gold and which contained baffles and seed supports made from either platinum or gold-plated silver. The publication by Armington et al. discusses the use of autoclaves with inert liners and the effects of the addition of lithium to the mineralizer.
Nevertheless, there remains a continuing need for methods and apparatus suitable for the inexpensive commercial production of high perfection quartz.